CONDENSED CONSOLIDATED STATEMENT OF INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Sales	$ 10,872	$ 11,760	$ 22,929	$ 22,575
Costs, Expenses and Other
Cost of sales	3,159	3,401	6,471	6,453
Selling, general and administrative	2,378	2,712	4,933	5,138
Research and development	2,123	2,189	4,331	4,119
Restructuring costs	83	59	155	212
Other (income) expense, net	(390)	140	(318)	327
Total Costs, Expenses and Other	7,353	8,501	15,572	16,249
Income Before Taxes	3,519	3,259	7,357	6,326
Taxes on Income	509	615	1,128	820
Net Income	3,010	2,644	6,229	5,506
Less: Net Income (Loss) Attributable to Noncontrolling Interests	8	(26)	8	(79)
Net Income Attributable to Merck & Co., Inc.	$ 3,002	$ 2,670	$ 6,221	$ 5,585
Basic Earnings per Common Share Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 1.19	$ 1.04	$ 2.46	$ 2.17
Earnings per Common Share Assuming Dilution Attributable to Merck & Co., Inc. Common Shareholders (in dollars per share)	$ 1.18	$ 1.03	$ 2.45	$ 2.15